1. Field of the Invention
The present invention generally relates to semiconductor processing. Specifically, the present invention relates to a turbo-molecular vacuum pump for evacuating a vacuum processing chamber used in semiconductor processing.
2. Background of the Related Art
Substrates are typically processed through various etch, chemical vapor deposition (CVD), physical vapor deposition (PVD), and cleaning steps to construct integrated circuits or other structures thereon. These steps are usually performed in an environmentally isolated and vacuum sealed substrate processing chamber. The substrate processing chamber generally comprises an enclosure having a side wall, a bottom and a lid. A substrate support member is disposed within the chamber to secure a substrate in place during processing by electrical or mechanical means such as an electrostatic chuck or a vacuum chuck. A slit valve is disposed on a chamber side wall to allow the transfer of the substrate into and out of the substrate processing chamber. Various process gases enter into the substrate processing chamber through a gas inlet, such as a shower-head type gas inlet, disposed through the lid of the processing chamber. To exhaust the gases from the substrate processing chamber, a vacuum pump, such as a turbo-molecular pump, is attached to a gas outlet of the substrate processing chamber.
Substrate processes such as plasma-based etch and CVD, are critically dependent on the reaction of gas molecules and reactive ions at the substrate surface because the concentration, the arrival rate and the directionality of the reactive gases and ions determine the process parameters such as the etch rate, the etch profile, the deposition rate, the deposition profile, the step coverage and the process uniformity. These parameters are usually controlled by the flow rates of the process gases and the chamber pressure, as well as the energy of the plasma and the distance of the plasma from the substrate. Particularly, the plasma-based etch and CVD processes require high process gas flow rates and relatively shallow vacuum levels. As the flow rate of the reactants across the substrate processing surface is increased (i.e., the throughput of the vacuum pump increases to exhaust a higher volume), the time required for completion of the process is reduced. Thus, to increase throughput of the processing chamber, the vacuum pumping system used for plasma-based etch and CVD, particularly for high density plasma (HDP) processes, must have a high throughput or exhaust capacity. Furthermore, as the chamber sizes increase to accommodate larger substrates (i.e., 300 mm substrates), the vacuum pumps, such as turbo-molecular pumps, used for these larger chambers must provide correspondingly larger exhaust capacities.
To increase the throughput or exhaust capacity of the vacuum pump and to decrease the time it takes to exhaust gases from a processing chamber, the pump size (i.e., physical capacity and size) of the turbo-molecular pump is typically enlarged. However, implementing larger pumps on existing systems often requires expensive and time-consuming retrofits such as pipe fittings that are required to provide the transition from the gas outlet of the chamber to the gas inlet of the larger turbo-molecular pump. Furthermore, larger pumps are typically more expensive and require larger "footprints" of the processing system. Larger footprints occupy more valuable clean-room space and may also require reconfiguration of the processing equipment.
Another way to decrease exhaust time and increase throughput of the pump is to increase the rotational speed of the rotor of the turbo-molecular pump. However, because of the high throughput of the process gases through the vacuum pump, unused reactants as well as reaction byproducts are removed from the processing chamber at a high rate and can either adhere to or react with the surfaces of the components inside the vacuum pump, causing the components to heat up significantly and resulting in breakdown of the component as well as the pump. For example, in HDP applications, the pump internal components, such as a rotor, can heat above 120.degree. C., and the stress caused by the high temperature causes physical break down of the component and the pump.
Therefore, there is a need for a turbo-molecular vacuum pump that provides a higher exhaust capacity than existing turbo-molecular pumps of approximately same physical sizes. In addition, there is a need for such a turbo-molecular pump that can be retrofitted onto existing processing chambers to improve throughput of existing systems.